1. Field of the Invention
The invention relates to a method and a system for manufacturing an optical display panel including an optical cell, such as a liquid crystal cell or an electroluminescent (EL) display cell, and an optical film provided on the surface of the optical cell.
2. Description of the Related Art
One of liquid crystal display (LCD) device manufacturing steps includes a bonding step in which multilayer optical films each having a polarizing film are bonded to both sides of a liquid crystal cell, which includes a pair of substrates and a liquid crystal layer sandwiched therebetween. In general, such multilayer optical films include a polarizing film and an adhesive or pressure-sensitive adhesive layer formed on at least one surface of the polarizing film, and thus can be bonded to the surface of a liquid crystal cell with the adhesive or pressure-sensitive adhesive interposed therebetween.
A method used for bonding such optical films to a liquid crystal cell includes feeding an optical film and a liquid crystal cell in the same direction and press-bonding the optical film to the liquid crystal cell, while superposing them. Specifically, a known method includes feeding a liquid crystal cell and an optical film between a pair of rollers opposed to each other and placed perpendicular to the direction of feed of the liquid crystal cell and the optical film, such as a pair of a guide roller for feeding the liquid crystal cell and a bonding roller for press-bonding the optical film to the liquid crystal cell, while superposing them; and press-bonding the optical film to the liquid crystal cell. In this case, the pressure-sensitive adhesive layer formed on the optical film may be covered with a peelable release film, and the optical film may be bonded to the liquid crystal cell by the above step, while or after the release film is peeled off. Examples of such a liquid crystal display device manufacturing method include a piece-by-piece manufacturing method in which optical film pieces formed by previously cutting an optical film into pieces of a predetermined size are each bonded to a liquid crystal cell by the above method; and a continuous manufacturing method in which optical film pieces formed by half-cutting are continuously supplied on a carrier film and each bonded (see, for example, Japanese Patent No. 4361103).
The latter continuous manufacturing method enables a continuous process of bonding between a liquid crystal cell and an optical film and therefore is significantly advantageous in terms of mass productivity or yield as compared with the conventional piece-by-piece method. A method for continuously manufacturing a liquid crystal display device includes providing a roll of a long multilayer optical film including a long carrier film and a long pressure-sensitive adhesive-carrying optical film placed on the carrier film with the pressure-sensitive adhesive interposed therebetween, cutting the long optical film to form predetermined sized pieces of the optical film on the long carrier film, while unwinding the multilayer optical film from the roll, and feeding the carrier film so that the pieces are continuously supplied to the bonding position.
Usually, such a roll of a multilayer optical film has a width corresponding to the length of one side of a rectangular liquid crystal cell. On the other hand, the long optical film, which is part of the multilayer optical film unwound from the roll, is cut into a piece with a length corresponding to the length of another side of the liquid crystal cell, so that the resulting piece of the optical film has the size of the liquid crystal cell. The piece of the optical film obtained by cutting into a size corresponding to that of the liquid crystal cell is fed to the step of bonding to the liquid crystal cell, as it is formed on the carrier film, and bonded to the liquid crystal cell. In the bonding step, the piece of the optical film fed on the carrier film is supplied to a bonding unit while it is peeled off from the carrier film, and the piece of the optical film and the optical cell, which is sequentially fed, are placed between a pair of pressing units and pressed by the pressing units, so that the piece of the optical film is bonded to at least one side of the liquid crystal cell with the pressure-sensitive adhesive layer of the optical film interposed therebetween. Such a pair of pressing units usually includes a pair of rolls, which is configured to feed the liquid crystal cell and the piece of the optical film while pressing them and to continuously press and bond the piece of the optical film from one end of the piece to the other.
On the other hand, an EL display panel produced with an organic or inorganic EL device often has a metal back electrode usually in order to increase the quantum efficiency of the luminescence or to increase the quantity of light output from the front side by reflection. EL display devices are characterized by achieving a very high display contrast ratio, but such characteristics are achieved only in a darkroom. In a usual environment for display view, external light such as light from indoor lighting is reflected by the back electrode of an EL display device to significantly reduce the contrast ratio and the display quality. To prevent a back electrode from reflecting external light, therefore, an anti-reflection film for circular polarization is bonded to the viewer-side surface of an EL display panel. Such an anti-reflection film includes a polarizing film and a retardation film, in which their absorption and slow axes should be ideally arranged at an angle of 45°, and the retardation film should be a quarter wavelength plate to produce a retardation. To improve productivity, it is also preferable to use a continuous manufacturing method in bonding an anti-reflection film to an EL display device. However, there has not been known any application of the above continuous liquid crystal display device-manufacturing method in manufacturing an EL display device.
It is also disclosed that pieces of optical film are formed in advance on a carrier film by cutting a long optical film (having a pressure-sensitive adhesive layer) as part of a long multilayer optical film and a roll of the product including the carrier film and the pieces formed thereon is put to use (see, for example, Japanese Patent No. 4503693).
The manufacturing apparatus for use in the above continuous manufacturing method has been required to be as compact in size as possible in view of production efficiency per area. There is also an increasing demand for high-throughput, high-yield bonding between an optical film and an optical cell in such a method for continuous manufacturing of an optical display panel.